Voltage-limiting device



Patented Apr. 6, 1926.

UNITED STATES- 1 time PATENT FFIQ WILLIAM A. KNOOP, OF EAST NORTHPORT, NEW YORK, ASSIGNOR TO \VESTERN ELECF TRIO COMPANY, INGORPORATE D, OF' NEW YORK, N. Y.,, A CORPORATION OF NEW YORK.

voL'rAen-LiMITINe nnvron.

Application filed July 22, 1922. Serial No. 576,682.

To all whom it may 0011061 1 1:

Be it known that I, VVILLIAM A. KNOOP, a citizen of the United States, residingat East Northport, in the county of Sulfolk, State of New York, have invented certain new and useful Improvements in Voltage- Limiting Devices, of which the following is a full, clear, concise, and exactidescription.

This invention relates to voltage limiting devices. s

In the operation of telephone circuits, such, for example, as long circuits which are exposed to inductive interferenceby neighboring power circuits operated at relatively high potentials, trouble known as acoustic shock is occasionally experienced, particularly by telephone operators, when a high potential surge is set up in the exposed circuit, due, for example, to the accidental grounding of the power circuit. The abnormal potential induced in the telephone line circuit produces an abnormal click in the telephone head receiver of the operator. The

result of such acoustic shock interferes with the normal operating routine and, therefore, is detrimental to the service.

It is an object of this invention to provide means for limiting the potentials due to the above and similar causes, that may beimpressed by a line circuit upon a telephone circuit, so that the current in the receiver can neverexceed a predetermined value regardless of the potential applied across the line circuit, thereby preventing what is known as acoustic shock. 1

In the form of the invention hereinafter described in detail, this is accomplished by connecting a spark gap or other discharge device effectively in shunt to the operators receiver, the break-down voltage of the de-.

Referring to the drawings, Fig. l repreobject of the invention is eifec sents this invention embodied in a switchboard circuit forprotecting a telephone operators receiver from excessive line p0- tentials. Fig. 2 illustrates by curves how the arrangement of this invention prevents excessive potentials from causing acoustic shock.

Fig. 1 of the drawing illustrates a telephone or other signaling line circuit 4, which is exposed to inductive interference fromfan adjacent power circuit 5. The line circuit 1 is connected by-means of a transformer 6 with a switchboard circuit 7, which has connected thereto an anti-side tone operators telephone set comprising a transmitter 8 and a receiver9 connected in a well-known manner to avoid side tone. {16 is the usual subset repeating coil and resistance 17' is employed in circuit with one side of the repeating coil to balance the impedance of the incoming line. The block 21 is intended to represent the usual signaling apparatus employed by the operator. 1

' Although the circuit 7 has been referred to as a switchboard circuit, it is to be under-' stood that this may be any circuit,as, for example,the circuit extending to a subscriber. But since the effective acoustic shock is usually most severe in the operators tele phone sets, the invention has, therefore, been described in connection with a switchboard circuit and the associated operators telephone set.

In accordance with this invention the low voltage winding 10 of a step-up transformer is connectedacross the terminals of the tele phone receiver 9, and the high voltage winding 11. of the transformer is connected to the electrodes of a spark gap or vacuum discharge tube 12. The ratio of transformation of the step-up transformershould be such that for normal moderate potentials impressed upon receiver 9 from the main line circuitat, the potential developed in winding 11 is not suilicient to cause an appreciable discharge to take place between the electrodes of device 12. When, however, excessive potentials, above 15 to 50 volts for example, tend to be im-pressed' upon receiver. 9 of suflioient "strength to cause sounds of abnormal strengtheto be emitted by the receiver, the potential de: veloped in Winding 11 should be suflicient- 1y highto cause the discharge to take place i charge should start.

I pending application of Frank Gray, Serial in device 12, thereby shunting away from ble of embodiment in other forms and arthe telephone receiver the excessive power which would tend to produce acoustic shock.

Device 12 may be any one of several types of discharge devices dependent upon the potential at which it is desired that the dis:

The device, for example, may comprise a tube enclosing the electrodes substantially at atmospheric pressure, or the device may be'a highly evacuated tube. One satisfactory device has been found to comprise a tube having its electrodes immersed in an atmosphere of heliumat a pressure of approximately two millimeters of mercury. A device of this character is shown and described in the co;

No. 604:,152, filed-December 1, 1922. It is preferable, of course, that the character oi? the device should be such that for moderate potentials impressed on the receiver only a small or negligible loss 1n transmission is incurred due to the presence of the protecting transformer and spark gap. The step-up transformer also should be designed to avoid an appreciable loss of transmission at times when only moderate potentials are present in the main line circuit 4:.

The manner in which this invention operates to shunt away the high potentials from the telephone receiver is illustrated by the curves of Fig. 2 in which the abscissae represent various values of the voltage present in the main line circuit 4 and the or dinates represent the volume of sound in.

the associated telephone receiver. As shown by the dotted line 14, the volume of sound in the receiver is roughly proportional to the impressed voltage in the absence of the protecting arrangement of this invention, and a high voltage present in line 4 will mean an abnormal volume of sound from the receiver. If, however, the receiver is shunted by the arrangement illustrated in Fig. 1 so that the excessive potentials are al sorbed by the spark gap, the character of the volume of sound obtained in the receiver for various line voltages is illustrated by the full line curve 15, the point where the full line curve 15 breaks away from the dotted line 14 indicating the point at which a discharge starts in the spark gap 12.

It is preferable that a switch be provided for disconnecting the receiver and the discharge tube from the line at, whenever signaling currents are applied to the line by the associated signaling apparatus. For this purpose the circuit may be broken at the points 19, 20 when outgoing ringing cur-- rent is applied to the line 4;, i. The potentials of the outgoing ringing currents are usually of the order of 100 volts.

Although this invention has been disclosed as embodymga particular circuit-arra-ngement it is to be noted that it is capa-' rangements without departing from the spirit and scope of the appended claims.

The invention claimed is:

1. In combination, a line, a telephone receiver, a step-up transformer having a low voltage Winding connected effectively in shunt to said receiver and a high voltage winding, and means associated with said high voltage windingfor closing the circuit thereof when the potential therein exceeds a predetermined value.

2. In combination, a line, a telephone receiver and means for protecting said receiver from excessive voltages in said line, said meanscomprising a transformer having a low voltage winding in circuit with said line and a high voltage Winding substantially open-circuited when said line is in use, and means associated with said high voltage winding for closing the circuit thereof when the a predetermined value.

3. In combination, a line, a telephone receiver, and means for protecting said -receiver from excessive voltages in said line,

said means comprising a step-up transformer having a low voltage winding connected effectively in shunt to said receiver and a high voltage Winding, and an electric discharge device comprising avessel evacuated to a pressure less than atmospheric pressure connected to the terminals of said high voltage winding, the voltage ratio of said transformer and the breakdown voltage of said electric discharge device being so adjusted that said receiver is effectively short-circuited for all line potentials in excess of volts.

4. In combination, a line, a telephone receiver, an electric dischargedevice comprising a vessel evacuated to a pressure less than atmospheric pressure, and means inductively associated with said line for causing said discharge device to function when voltages in excess of 15 volts exist in said line to prevent said voltages from being translated into sound b said receiver,

5. In com ination, a signaling line exposed to inductive interference, a switchboard cicuit connected to said line a telephone receiver connected to said switchboard circuit, a step-up transformer having a low voltage winding connected eflectively across said line, said transformer having a high voltage winding substantially open-circuited as long as moderate voltages are present in said line, and means for completing the circuit of said high voltage winding when excessive potentials are present in said line.

6. In combination, a line, a substation cir cuit comprising a receiver and signaling apparatus, a protective device connected effectively in shunt to said receiver, the break down potential of said protective device bepotential therein exceeds ing lower than the potentials used in signaling, and means for breaking the circuit between said signaling apparatus and said protective device.

7. In combination, a line, a substation circuit comprising a receiver and signaling apparatus, a protective device comprising a step-up transformer having a low voltage winding connected in shunt to said receiver and an electric discharge device comprising a vessel evacuated to a pressure less than atmospheric pressure connected to the high voltage terminals of said transformer, the breakdown voltage of said protective device being lower than the potentials used in signaling and means for breaking the circuit between said signaling apparatus and said protective device.

In witness whereof, I hereunto subscribe my name this 19th day of July, A. D. 1922.

WILLIAM A. KNOOP. 

